Methods of removing copper and related metals from sulfidic molybdenum ores and molybdenum-containing materials



United States Patent METHQDS 0F REMOVING COPPER AND RELATED METALS FROM SULFIDIC MOLYBDENUM ORES AND MQLYBDENUM-CONTAINING MA- TERIALS Lars Roland Bjerkerud, Trollhattan, Olof Ragnar Drakenberg, Stockholm, and Gerhard Sixtensson von Hofsten, Trolihattan, Sweden, assignors to Ferrolegeringar Trollhatteverken Aktiebolag, Trollhattan, Sweden, a corporation of Sweden No Drawing. Filed Aug. 28, 1961, Ser. No. 134,122

Claims priority, application Sweden Apr. 11, 1958 Claims. (Cl. 75-113) The present invention relates generally to the art of recovering molybdenum from molybdenum-containing raw materials of sulfidic nature and is more particularly concerned with a method of removing copper and related metals from such materials before recovering of molybdenum therefrom.

This application is a continuation-in-part of our copending application Serial No. 800,925, filed on March 23, 1959.

Molybdenum is obtained in addition to its recovering from ores which are mined primarily or exclusively on account of their content of molybdenum to a great extent, also as a by-product in the enrichment of other ores, mainly copper ores but also tungsten ores. According to a survey (W. Mclnnins, Molybdenum A Materials Survey, Bureal of Mines Information Circular 7784, 195-7) in 1955 about 40% of the words production of molybdenum derived from ores of the last-mentioned types. Of those ores which yield molybdenum as a by-product the copper ores are the most important from a commercial point of view. The molybdenum is present in these ores as molybdenum sulfide, M05 and the molybdenum content is generally low, about of the copper content. In the enrichment of the copper ores, which is carried out by flotation, the molybdenum sulfide is separated as a concentrate which, however, has a high content of the copper mineral and usually also'a minor content of ferrous minerals. An example of the composition of such a concentrate is 41% of Mo, 9% of Cu and 6% of Fe, by weight. Other minerals which may be present in such ores are bismuth and lead sulfides.

The separation of molybednum from the copper is difiicult but is necessary in order that the molybdenum concentrate shall be useful for the production of technical molybdenum oxide (M00 ferromolybdenum etc. When these materials are to be used in the iron and steel industry it is required that the copper content is low, usually not more than 1% of the molybdenum content. In some cases it is even required that the copper content is still lower, e.g., not more than /a% of the content of molybdenum.

To separate the copper from the molybdenum concentrate, a number of methods are used in practice. The Bureau of Mines publication referred to above describes the usual methods. A common characteristic of these methods is that the material is subjected to repeated flotation steps, usually at least four steps. The treatment is concluded by a subsequent leaching with cyanide solutions or sulfuric acid. In some cases the material is subjected to heat-treatment between the flotation steps. A disadvantage of these processes, apart from the complicated and costly procedure, is that no sharp separation between molybdenum and copper is achieved. Many processes have been suggested to eliminate these disadvantages (see, e.g., US. Patents 2,492,936, 2,187,930, 2,095,967, 2,599,104, 2,255,776 and 2,664,199) but in no case an economically and practically advantageous solution of the problem has been achieved.

The main object of the present invention is to provide silicic gangue present in the original material.

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a method of separating copper and also related metals, such as bismuth and lead, from molybdenum-containing sulfidic ores and other molybdenum-containing sulfidic materials, which method is free from the objections and disadvantages of prior art methods and results in a sharp separation or" the copper from molybdenum in an efiicient and economical way. Other objects and advantages of the invention will appear as the description proceeds.

The invention is based upon the unexpected discovery that it dry sulfidic materials containing copper and molybdenum are treated with gaseous chlorine, either pure gaseous chlorine or a gas mixture containing chlorine, the copper compounds of the mixture react with the chlorine to form water-soluble copper chlorides, while provided that the reaction is carried out below a certain temperature, the molybdenum compounds do not react appreciably with the chlorine but remain unreacted and therefore insoluble in water. Thus, it is possible after a chloridizing reaction in this manner to separate the copper and molybdenum content simply by leaching with water to leach out the water-soluble copper chlorides, leaving the water insoluble molybdenum compounds in the leaching residue. It was also found that bismuth and lead sulfides, if present, react in the same manner as copper in the chloridizing treatment, so that they can also be separated from the molybdenum-containing sulfidic material by chloridizing and leaching.

Accordingly, this invention relates to a method of treatin a sulfide material comprising molybdenum together with at least one metal of the group consisting of copper, bismuth and lead, to remove said metal from the material, said method comprising reacting the sulfidic material with gaseous chlorine at a temperature not above 400 C. and such that the molybdenum content is not appreciably attacked by the chlorine, while said metal is converted substantially completely into a water-soluble chloride, and leaching the resulting mixture with an aqueous liquid to remove said water-soluble chloride. Iron, if present in the raw material is generally at least partly converted into a water-soluble chloride and a portion of the iron will therefore generally be removed together with the copper, bismuth or lead. From the leaching solution copper, lead or bismuth can be recovered as chloride or in metallic form by known methods. The leaching residue contains unchanged molybdenum sulfide and any Since in addition to copper, bismuth or lead a considerable amount of iron is generally removed, the molybdenum content of the molybdenum concentrate is increased, which is advantageous for its subsequent use and enhances its commercial value. The molybdenum concentrate obtained may be worked in the usual manner to recover molybdenum, e.g., as molybdenum oxide or metallic molybdenum.

The chloridizing reaction is rapid and relatively unaffected by variations in temperature, composition of the gas and composition of the material treated. Thus, the temperature may normally vary from about 150 to 300 C. The most favorable temperature varies somewhat with the composition of the gas. Thus, it has been established that for some ores a suitable temperature when pure gaseous chlorine is used is 150-200 C., while for the same ores 200-250 C. is the most favorable tempera ture when the chlorine gas is diluted with of nitrogen.

Also, the most favorable temperature appears to vary somewhat with the composition of the ore depending on whether it contains copper as a double salt, such as chalcopyrite (CuFeS or as an oxide or sulfide (chalcosite C1128).

The composition of the gas can vary within Wide limits, e.g. from 10 to of Cl The presence of oxygen can be tolerated to a certain extent, but it is to be noted that presence of oxygen can in some cases cause oxidation of some copper resulting in formation of a copper oxychioride which is insoluble in water and also in oxidation of some molybdenum to form molybdenum oxide which is soluble in water, so that presence of oxygen may lower the efiiciency of separation. Therefore, oxygen should preferably be excluded from the reaction vessel, which is easily achieved by maintaining a pressure slightly above atmospheric in the reaction vessel to avoid leakage of air thereinto. A small amount of oxygen, e.g., up to 5 or however, is in most cases permissible.

The composition of the starting material can be varied within wide limits. For example, the molybdenum content may vary from about 10 to about 60%, the total content of copper, lead and bismuth may vary from about 1 to about 20% and the iron content from 0 to 10%.

The chloridizing reaction is rapid and normally the necessary time of reaction does not exceed minutes.

On an industrial scale the process can advantageously be carried out in a rotary furnace, through which the material to be treated and the chlorine-containing gas move in countercurrent or cocurrent to each other. The furnace construction may be very simple. It may be unlined since no serious reaction between the chlorine and the furnace material (steel) takes place at the temperatures involved. The furnace may be externally heated or the material or the gas or both may be heated before introduction into the furnace. The process can also be carried out in other equipment, e.g., in multiple hearth furnaces or in fiuidization apparatus. The apparatus chosen depends partly on the type and composition of the starting material involved.

The process of this invention is illustrated but not limited by the fol-lowing examples wherein percentages are by weight except where otherwise noted.

EXAMPLE 1 4 grams of a sulfidic molybdenum ore concentrate containing 41.03 Mo, 9.22% Cu and 5.95% Fe were placed in a porcelain boat and were treated for 15 minutes at 200 C. in a resistance-winded laboratory tubular furnace with pure gaseous chlorine which was passed through the furnace. The boat was removed from the furnace and after cooling the material was leached with 200 cc. of water at room temperature. Thereby, about 3 g. of leaching residue were obtained which contained 55.72% M0, 0.01% Cu and 1.06% Fe. The yield of molybdenum in the leaching residue amounted to above 99.9%. Based on the original material 0.04% of the molybdenum, 8.40% of the copper and 4.58% of the iron were found in the leaching liquid. The yield of molybdenum therein is less than 0.1%, the yield of copper 91.8% and the yield of iron 77.1%.

EXAMPLE 2 In a resistance heated rotary furnace of about 1.5 meter (length and 110 mm. diameter another sulfidic material containing 32.7% Mo, 1.52% Cu and 8.6% Fe was treated with a mixture of by volume of chlorine and 80% of air in countercurrent. The furnace temperature was 175 C., the speed of revolution was 8 r.p.m. and the capacity of the rotary furnace was such as to obtain about 500 g. of chloridized ore per hour. 'The amount of chlorine gas corresponded to about in excess of that stoichiometrically required for complete chlorination of the copper and iron content. 1 kilogram of the chloridized material was leached with 3 liters of water. The leaching residue contained 38.0% Mo, 0.10% Cu and 4.0% Fe. Based on the original material, 0.00%

V of the molybdenum, 1.42% of the copper and 2.57% of The molybthe copper yield 93.4%

ages

4 EXAMPLE 3 In a resistance-heated rotary furnace of 6 m. length and 300 mm. diameter rotating with a speed of 3 r.p.rn., 100 kg./h. of the starting material, a molybdenum material, the contents of Mo, Cu and Fe of which are indicated below, were fed. In countercurrent thereto was passed pure gaseous chlorine in an amount corresponding to grams per kg. of ore. The furnace is along 1ts length divided into several electric thermostat-controlled heating sections, because the exothermal character of the process sometimes causes hot spots which must be counteracted by cutting out the resistance heating of these furnace sections. The temperature measured with thermocouples within the furnace was controlled at the material intake end to 200 C. and at the material discharge end to 250 C.

kg. of the discharged material which was received in a gas tight closed container was leached in 400 liters of water, whereupon the leaching residue and the leaching liquid had the contents of Mo, Cu and Fe as shown in the table. The corresponding yields in the leaching liquid were 0.02% Mo, 87.9% Cu and 19.5% Fe.

In a chloridizing operation corresponding to that described in Example 1 there was used at the starting material a sulfidic ore containing 53.5% Mo, 0.035% Cu, 320% Bi and 0.40% Pb. After chlorinating in pure gaseous chlorine for 30 minutes at 220 C. and leaching in Warm water the leaching residue was analysed and contained 0.04% Bi and 0.15% Pb.

It is readily apparent from the first three examples above that the removal of copper takes place very easily whether the operation is carried out on a large scale or on a small scale and also that the apparatus may, in principle, be very simple. That bismuth and lead may be removed in the same manner as copper from a molybdenum ore by the same process is evident from Ex ample 4.

'5 course, the corresponding operations can be carried out in more complex apparatus, such as multiple hearth furnace or iiuosolid furnaces, as will be obvious to those skilled in the art. It is also readily apparent to those skilled in the art that in an industrial plant chloridizing, leaching and precipitation of copper may becarried out continuously in a series of production units. T his does not change the principle of the invention. 4

(Ether modifications and variations are possible without departing from the spirit and scope of the invention.

We claim:

1. A method for treating molybdenum sulfide materials containing as an impurity at least one metal from the group consisting of copper, bismuth and lead, to remove said impurity therefrom which comprises heating said materials to a temperature of at least C. but not above 400 C., passing dry gaseous chlorine in the presence of not over 10% oxygen through said heated materials for a time sufiicient to effect chloridizing of said impurities but insutficient to effect chioridizing of the.

sulfide material.

2.- The method according to claim 1 in which the ma- 7 5 terial is heated to a temperature within the range 150- 250 C.

3. The method according to claim 2 in which the chlorine is substantially free of oxygen.

4. The method according to claim 1 in which the material is treated with chlorine in a fluidized bed.

5. The method according to claim 1 in which the material is treated at a temperature in the range of 200- 250 C. with a mixture of chlorine and an inert diluent gas.

References flied in the file of this patent UNITED STATES PATENTS 

1. A METHOD FOR TREATING MOLYBDENUM SULFIDE MATERIALS CONTAINING AS AN IMPURITY AT LEAST ONE METAL FROM THE GROUP CONSISTING OF COPPER, BISMUTH AND LEAD, TO REMOVE SAID IMPURITY THEREFROM WHICH COMPRISES HEATING SAID MATERIALS TO A TEMPERATURE OF AT LEAST 150*C. BUT NOT ABOVE 400*C., PASSING DRY GASEOUS CHLORINE IN THE PRESENCE OF NOT OVER 10% OXYGEN THROUGH SAID HEATED MATERIALS FOR A TIME SUFFICIENT TO EFFECT CHLORIDIZING OF SAID IMPURITIES BUT INSUFFICIENT TO EFFECT CHLORIDIZING OF THE MOLYBDENUM MATERIALS WHEREBY SAID METAL IMPURITY REACTS WITH CHLORINE TO FORM THE CORRESPONDING CHLORIDE SALT, COOLING THE THUS TREATED ORE, LEACHING THE TREATED MATERIAL WITH AN AQUEOUS LIQUID TO REMOVE CHLORIDE SALTS THEREFROM, AND RECOVERING THE THEREBY ENRICHED MOLYBDENUM SULFIDE MATERIAL. 